Engines may be configured to operate with fuels that can range from low concentrations of alcohol mixed with gasoline to fuels that have relatively high concentrations of alcohol mixed with gasoline. For example, a so called flexible fuel vehicle can operate with fuel comprised completely of gasoline or a fuel comprised of 85% ethanol and 15% gasoline. If the engine is controlled to operate substantially the same (e.g., with no difference in spark timing) and independent of the concentration of alcohol in the fuel, engine fuel economy may be reduced when fuels having higher alcohol concentrations are combusted. Therefore, it may be desirable to accurately determine a concentration of alcohol in fuel being combusted. One way of determining alcohol content in fuel is to place a sensor in the fuel so that alcohol may be detected in the fuel. However, alcohol sensors can add cost to a vehicle and they also increase engine system complexity.
The inventors herein have recognized the above-mentioned limitations and have developed a method for operating an engine, comprising: adjusting an engine actuator in response to an alcohol concentration of a fuel combusted by the engine, the alcohol concentration based on a position of a throttle, an output of an exhaust gas oxygen sensor, engine speed, and a fuel injector pulse width.
Alcohol concentration of a fuel may be determined without a dedicated fuel composition sensor. In one example, alcohol concentration of a fuel combusted in an engine can be determined via fuel pulse width, engine speed, engine air intake throttle position, and a lambda value from an exhaust gas oxygen sensor. Thus, alcohol concentration of a fuel may be determined via sensors commonly found in a fuel injected engine. In this way, engine system cost and complexity may be reduced for engines that combust a mixture of gasoline and alcohol.
The present description may provide several advantages. Specifically, the approach may provide an alcohol concentration of a fuel without a dedicated fuel composition sensor. Further, the approach may be useful for providing compensation for errors in the engine air intake system and the engine fuel system.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.